add TestConfigBuilder interface to clusterapi

This change converts the previous single function interfaces to create
machineset and machinedeployment test configs to instead use a new
builder/fluent style interface. This make the tests easier to read and
simpler to contribute new functionality.
The previous functions have been migrated to a new file to help keep the
complexity from overlapping into other test functions, and to promote
future refactoring.

Author: elmiko

cluster-autoscaler/cloudprovider/clusterapi/clusterapi_autodiscovery_test.go

@@ -198,7 +198,7 @@ func Test_parseAutoDiscovery(t *testing.T) {
 func Test_allowedByAutoDiscoverySpec(t *testing.T) {
 	for _, tc := range []struct {
 		name                string
-		testSpec            testSpec
+		testSpec            TestSpec
 		autoDiscoveryConfig *clusterAPIAutoDiscoveryConfig
 		additionalLabels    map[string]string
 		shouldMatch         bool